How can I measure SMA devices with Agilent 85033E 3.5 mm cal kit?

I've got an HP 8720D VNA and Agilent 85033E calibration kit, and want to measure an SMA female device. That device is actually an SMA short and I want to find the distance between the reference plane and the short. But the results I'm getting don't look too good, and I suspect its due to the mis-match between SMA and 3.5 mm, but I may be wrong. But I don't know how best to correct this, or at least reduce its effects. If I take the *3.5 mm female short standard* from the 85033E calibration kit, and apply a port extension equal to the offset delay of the short, then on the Smith Chart the device looks like a dot on the left. No great surprise that If I now replace the 3.5 mm short with an *SMA female short*, I am unable to find any port extension at which the Smith Chart shows a dot on the left. The Smith Chart view (hand edited as my software was not displaying it very clearly), shows the view with a port extension of 25.854 ps. Note the phase first goes in one direction then changes direction around 3.5 GHz. It should be easier to see on the graphs plotted with Excel. Any thoughts on what I can do to find the offset delay of this SMA female short? I've attached two Touchstone files. * sma-short-0ps.s2p is the SMA short measured with *no port extensions*. * sma-short-25.854ps is the SMA short measured with *25.854 ps port extensions* Has anyone any comments as to whether my results are surprising, or what (if anything) can be done to improve matters. Perhaps I am just asking too much of a non-precision connector. Dave

Looks like I'll have the same issues. See my post in the calibration sub-forum about creating an SMA cal kit. I suppose you could attempt to (circuit) model the response to see if the discontinuity is at the reference plane, such as a slight step in Z0, or inductance at the short (after the delay). I could probably do a rough model in my 3D EM software.

> {quote:title=MADENGR wrote:}{quote} > Looks like I'll have the same issues. See my post in the calibration sub-forum about creating an SMA cal kit. I suppose you could attempt to (circuit) model the response to see if the discontinuity is at the reference plane, such as a slight step in Z0, or inductance at the short (after the delay).

Part of my problem was the short was not very good. I later tried a better short, and things were not so bizzare, but I have not persued this any further.

I like your idea on the other thread of mercury for a zero length short! Of course mercuy does disolve gold, so perhaps the short gets shorter and shorter over time!

When I was a kid at school, someone in my class called Paul had a dad who was a scrap metal dealer. Paul said there was a sweet jar at home so full of mercury that was too heavy to lift. Quite often Paul would bring the mercuty into school and we would play with it, holding it in our hands, pouring it and getting it into lots of small volumes, then combining it to make it bigger. Nobody told us the stuff is toxic. So if any of my posts would indicate I am as mad as a hatter, you know why!

Ha ha, we had similar experiences with Mercury. I still have the 1 pound bottle I had when I was kid, and remember rolling it in the pencil troughs on the school desks.

I took your S2P file and repaired it into an S1P file. Since you are using # MHz S DB R 50 header you should use -99 for the dummy magnitudes instead of 0, otherwise the circuit simulators will freak out. I then applied the SMA-3.5mm reference plane discontinuity model (shunt C) from the paper Dr. Wong mentioned in the other thread.

The discontinuity model does not make much difference (1 degree) until you approach 6 GHz. I was able to pull the phase response into +/-1 degree by de-embedding 0.3 pH at the reference plane, which would indicate center pin set-back, but 0.3 nH seems like way too much The setback listed in the paper is 10 mils (0.254 mm), which is 0.18 nH using my rule of thumb for a bond wire, but again, it's in coax so it should not be that much. Moving the inductance to the other side of the delay, to de-embed it from the short standard, does not give as nice results.

Edited by: MADENGR on Jun 22, 2013 2:26 PM

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> {quote:title=MADENGR wrote:}{quote} > Ha ha, we had similar experiences with Mercury. I still have the 1 pound bottle I had when I was kid, and remember rolling it in the pencil troughs on the school desks.

Mercury sure is funny stuff. I don't know the risks with messing around with it as a kid. I know people who use it in their job (hat makers), did suffer the long-term effects - hence the term as "mad as a hatter", but perhaps the occasional messing around wont send us all to an early grave.

My old chemistry teacher used to be an industrial chemist. He apparently got mercury poisoning. Apparently they used to take finger nail cuttings to see the mercury in them. I can't recall him saying what the effects on him was.

> I took your S2P file and repaired it into an S1P file. Since you are using # MHz S DB R 50 header you should use -99 for the dummy magnitudes instead of 0, otherwise the circuit simulators will freak out.

Thank you. I wrote the program to generate the .s2p myself. It is a bit of C code which runs on a Sun workstation. I'll modify the code at some point and stick -99 in the unused magnitudes.

> I then applied the SMA-3.5mm reference plane discontinuity model (shunt C) from the paper Dr. Wong mentioned in the other thread.

I'll take a read of that paper.

> The discontinuity model does not make much difference (1 degree) until you approach 6 GHz. I was able to pull the phase response into +/-1 degree by de-embedding 0.3 pH at the reference plane, which would indicate center pin set-back, but 0.3 nH seems like way too much The setback listed in the paper is 10 mils (0.254 mm), which is 0.18 nH using my rule of thumb for a bond wire, but again, it's in coax so it should not be that much. Moving the inductance to the other side of the delay, to de-embed it from the short standard, does not give as nice results.

The short I used was quite poor. I had a number of shorts, some of which have 4 slots in the female, part, and the one I showed the results for has just two slots. I've never seen anything as bad before. I did not know this at the time I wrote that post. With a better short, the results were less bizzare, not rotating first once way, then the other around the Smith Chart.